Fuel cell systems convert a fuel and an oxidant to electricity in a fuel cell stack. One type of fuel cell system employs a proton exchange membrane (hereinafter “PEM”). The PEM is a solid polymer electrolyte membrane that facilitates transfer of protons from an anode to a cathode in each individual fuel cell normally deployed in a fuel cell system. The electrodes and membrane together form a membrane electrode assembly (MEA). The electrodes contain catalysts to catalytically facilitate reaction of the fuel (such as hydrogen) and the oxidant (such as oxygen or air) to generate the electricity.
In a typical PEM fuel cell, the MEA is disposed between gas diffusion media (GDM). The GDM and MEA are disposed between a pair of electrically conductive plates. If the plates are bipolar plates, the plates conduct current between adjacent fuel cells in the fuel cell system. If the plates are unipolar plates at an end of the fuel cell system, the plates conduct current externally of the fuel cells.
As described in applicant's co-pending U.S. patent application Ser. No. 11/762,845, hereby incorporated herein by reference in its entirety, the goal of an anode supply manifold purge operation is to completely fill the anode supply manifold with hydrogen prior to filling active areas of the anode with hydrogen during startup. Generally, the anode supply manifold is filled with hydrogen by opening a manifold purge valve at the top of the anode supply manifold while producing a flow of hydrogen into the bottom of the anode supply manifold.
A flow rate of hydrogen, along with a flow resistance of the purge valve, creates a back pressure in the anode supply. As the back pressure increases in the anode supply manifold, hydrogen in the bottom of the supply manifold is caused to flow into the active areas of fuel cell plates at the bottom of a fuel cell stack. As the hydrogen flows into the active areas of the fuel cell plates, a localized voltage rise may be measured. The voltage rise generates a current that is driven through the remaining fuel cell plates of the fuel cell stack. Fuel cells of the fuel cell stack which do not have a sufficient amount of hydrogen to support the current will experience a localized reversed current, thereby resulting in electrode carbon corrosion. Additionally, fuel cells without a sufficient amount of hydrogen are in a hydrogen deficit. To overcome the hydrogen deficit, additional hydrogen must be caused to flow into the fuel cell stack, thereby increasing a start-up time of the fuel cell system.
It would be desirable to develop a method for filling an anode supply manifold of a fuel cell system with hydrogen prior to a start-up operation, wherein the anode supply manifold is substantially evenly filled with hydrogen and unevenly filling an active area of fuel cells of the fuel cell stack with hydrogen is militated against.